1. Field of the Invention
The present invention relates to a reflector and a reflective liquid crystal display device, and more particularly to a reflector having characteristics of reflection that enable reflected light observed at a specific viewing angle to be more brightly viewed than light observed at other viewing angles, and a reflective liquid crystal display device using the reflector.
2. Description of the Related Art
In general, a reflective liquid crystal display device which facilitates viewing images by using external light or front light as an illuminating source has been widely used as a display unit for electronic apparatuses such as portable computers, electronic calculators, digital watches, communication apparatuses, game machines, measuring instruments, and electronic boards.
The reflective liquid crystal display device schematically comprises a light-transmissive display-side substrate 220 and a reflective reflection-side substrate 210 between which a liquid crystal layer 230 is interposed, as shown in the example in FIG. 12. An outer surface of the display-side substrate 220 is a display plane, and a reflecting layer 212 is provided on the reflection-side substrate 210. In the reflective liquid crystal display device, light which is incident on the display plane passes through the display-side substrate 220 and the liquid crystal layer 230, and reflects on the reflecting layer 212 of the reflection-side substrate 210. In turn, reflected light passes through the liquid crystal layer 230 and is emitted from the display plane, so that an image can be viewed.
Referring to FIG. 12, the reflection-side substrate 210 is constructed, from bottom to top, with a glass substrate 211, the reflecting layer 212, an interposing layer 213, a color filter layer 214, a planarized layer 215, a transparent electrode 216 made of ITO (indium tin oxide) film or NESA film, and an alignment layer 217. In addition, the display-side substrate 220 which is disposed to face the display plane through the liquid crystal layer 230, is constructed with an alignment layer 221, an insulating layer 222, a transparent electrode 223 made of ITO film or NESA film, a glass substrate 224, and an optical modulating layer (a polarizing plate, a phase difference plate, etc.) 225, being stacked in this order from the liquid crystal layer 230.
The reflecting layer 212 of the reflection-side substrate 210 may be roughly classified as either a smooth reflecting type or a diffusive reflecting type. In a smooth reflecting type, the reflecting plane of the reflecting layer 212 is smoothly finished, so that the incident angle (absolute value) and the emitting angle (absolute value) are the same based on the normal line, which is perpendicular to the display plane. Accordingly, as observed with display planes, there is a problem in that irregularity of brightness of the display plane occurs due to the relationship between the location of the light source and the location of the viewing point, In addition, there is another problem in that the light source or the observer's face occurs as a reflected image, thereby diminishing visibility.
In order to solve the above-mentioned problems, in a diffusive reflecting type, a plurality of minute concave/convex portions (concave portions 231 in FIG. 13) are disposed to be irregularly adjacent to the reflecting surface of the reflecting layer 212, as shown in FIG. 13. For this reason, in the diffusive reflecting type, external light which is incident at a predetermined angle is subjected to irregular reflection at the surface of the reflecting layer 212, and then the reflected light is diffused, and thus brightness is not greatly variant as the viewing point is shifted and a little of the reflected image occurs, so that the so-called wide-viewing-angle reflective liquid crystal display device can be implemented.
However, in such electronic apparatuses as table electronic calculators or portable computers, as shown in FIG. 14A regarding an example of the table calculator and in FIG. 14B regarding an example of the portable computer, the observer mainly views the display plane from a downwardly sloped direction. In other words, the viewing point Ob is downwardly-sloped from the display plane by an angle of θ to the normal line X, which is perpendicular to the display plane.
On the other hand, in a reflective liquid crystal display device, there are many cases in which illumination is performed by using external light, and external light is drastically attenuated in the course of reciprocally passing through an optical modulating layer 225 such as a polarizing plate, two layers of transparent electrodes 216 and 223, the liquid crystal layer-230, and other layers. In a diffusive liquid crystal display device, since incident light is widely diffused by the reflecting layer 212, the display screen at the viewing point Ob becomes relatively dark, in general. For this reason, if the amount of external light is small, visibility may be drastically diminished. In particular, in a conventional reflective liquid crystal display device, since the shape and locations of concave portions are designed to suppress variation of brightness according to the viewing angle as much as possible, there is a problem in that sufficient brightness can not be obtained when viewing in a specific viewing angle range, that is, a downwardly-sloped range to the normal line. In addition, even when using front light, there are the same problems of attenuation and diffusion of light as when using external light. Therefore, it is difficult to ensure sufficient brightness within a specific viewing angle range without uselessly increasing power consumption for illumination. On the other hand, in a reflective liquid crystal display device, there are many cases in which illumination is performed by using external light, and external light is drastically attenuated in the course of reciprocally passing through an optical modulating layer 225 such as a polarizing plate, two layers of transparent electrodes 216 and 223, the liquid crystal layer 214, and other layers. In a diffusive liquid crystal display device, since incident light is widely diffused by the reflecting layer 212, the display screen at the viewing point Ob becomes relatively dark, in general. For this reason, if the amount of external light is small, visibility may be drastically diminished. In particular, in a conventional reflective liquid crystal display device, since the shape and locations of concave portions are designed to suppress variation of brightness according to the viewing angle as much as possible, there is a problem in that sufficient brightness can not be obtained when viewing in a specific viewing angle range, that is, a downwardly-sloped range to the normal line. In addition, even when using front light, there are the same problems of attenuation and diffusion of light as when using external light. Therefore, it is difficult to ensure sufficient brightness within a specific viewing angle range without uselessly increasing power consumption for illumination.
Accordingly, a reflective liquid crystal display device capable of suppressing a reflected image within a wide viewing angle range and viewing a particularly bright display screen at a specific viewing angle has been needed.